Initial fixes based on feedback

Author: JimBobSquarePants

src/ImageSharp/Formats/Jpeg/Components/Block8x8F.Vector128.cs

@@ -1,6 +1,7 @@
 // Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
+using System.Numerics;
 using System.Runtime.CompilerServices;
 using System.Runtime.Intrinsics;
 using SixLabors.ImageSharp.Common.Helpers;
@@ -19,8 +20,8 @@ internal partial struct Block8x8F
     [MethodImpl(InliningOptions.ShortMethod)]
     public void NormalizeColorsAndRoundInPlaceVector128(float maximum)
     {
-        Vector128<float> off = Vector128.Create(MathF.Ceiling(maximum * 0.5F));
         Vector128<float> max = Vector128.Create(maximum);
+        Vector128<float> off = Vector128.Ceiling(max * .5F);
 
         this.V0L = NormalizeAndRoundVector128(this.V0L.AsVector128(), off, max).AsVector4();
         this.V0R = NormalizeAndRoundVector128(this.V0R.AsVector128(), off, max).AsVector4();

src/ImageSharp/Formats/Jpeg/Components/Block8x8F.Vector256.cs

@@ -46,8 +46,8 @@ internal partial struct Block8x8F
     [MethodImpl(InliningOptions.ShortMethod)]
     public void NormalizeColorsAndRoundInPlaceVector256(float maximum)
     {
-        Vector256<float> off = Vector256.Create(MathF.Ceiling(maximum * 0.5F));
         Vector256<float> max = Vector256.Create(maximum);
+        Vector256<float> off = Vector256.Ceiling(max * .5F);
 
         this.V256_0 = NormalizeAndRoundVector256(this.V256_0, off, max);
         this.V256_1 = NormalizeAndRoundVector256(this.V256_1, off, max);

src/ImageSharp/Formats/Jpeg/Components/Block8x8F.cs

@@ -488,18 +488,30 @@ public void LoadFromInt16Scalar(ref Block8x8 source)
     /// <param name="value">Value to compare to.</param>
     public bool EqualsToScalar(int value)
     {
-        // TODO: Can we provide a Vector128 implementation for this?
-        if (Avx2.IsSupported)
+        if (Vector256.IsHardwareAccelerated)
         {
-            const int equalityMask = unchecked((int)0b1111_1111_1111_1111_1111_1111_1111_1111);
-
             Vector256<int> targetVector = Vector256.Create(value);
             ref Vector256<float> blockStride = ref this.V256_0;
 
             for (nuint i = 0; i < RowCount; i++)
             {
-                Vector256<int> areEqual = Avx2.CompareEqual(Avx.ConvertToVector256Int32WithTruncation(Unsafe.Add(ref this.V256_0, i)), targetVector);
-                if (Avx2.MoveMask(areEqual.AsByte()) != equalityMask)
+                if (!Vector256.EqualsAll(Vector256.ConvertToInt32(Unsafe.Add(ref this.V256_0, i)), targetVector))
+                {
+                    return false;
+                }
+            }
+
+            return true;
+        }
+
+        if (Vector128.IsHardwareAccelerated)
+        {
+            Vector128<int> targetVector = Vector128.Create(value);
+            ref Vector4 blockStride = ref this.V0L;
+
+            for (nuint i = 0; i < RowCount * 2; i++)
+            {
+                if (!Vector128.EqualsAll(Vector128.ConvertToInt32(Unsafe.Add(ref this.V0L, i).AsVector128()), targetVector))
                 {
                     return false;
                 }

tests/ImageSharp.Tests/Formats/Jpg/Block8x8FTests.cs

@@ -462,7 +462,7 @@ static void RunTest()
         // 3. DisableAvx2 - call fallback code of float implementation
         FeatureTestRunner.RunWithHwIntrinsicsFeature(
             RunTest,
-            HwIntrinsics.AllowAll | HwIntrinsics.DisableAVX2);
+            HwIntrinsics.AllowAll | HwIntrinsics.DisableAVX | HwIntrinsics.DisableSSE);
     }
 
     [Theory]